Abstract: Gaps occurring between a cathode substrate and a gas housing in a fuel cell interfere with electron transfer in the cell causing high cell internal resistance. To reduce the high resistance gaps are closed by coating the substrate with metal powder that expands during oxidation closing the gaps.

Abstract: A beam of light issued by a light source enters a catadioptric arrangement and initially travels therethrough along an axis. At least one lens is situated at the axis and is axially delimited by two curved major surfaces having respective centers of curvature. The beam of light is reflectively diverted from the axis and travels in a path which includes a path section that is directed at one of the major surfaces and has such a spatial orientation relative to the axis and the major surfaces that light traveling in this path section bypasses the centers of curvature and impinges all regions of the major surfaces at angle deviating from respective normals to the regions with attendant avoidance of specular retroreflection from such regions.

Abstract: A turbine engine debris ingestion monitor has an acoustic emission sensor 18, 18a mounted on a surface 14, 14a disposed in an air flow stream of a turbine engine 12. The sensor converts acoustic emissions 16, generated by particles of debris 10 impacting on the surface, into an electrical signal. A counting circuit 22 (FIG. 2) processes the signal resulting in an output, indicative of the level of debris ingested into the engine, which is recorded in the aircraft's flight data recording system 110.

Abstract: An arrangement for forming an extended length light redirecting embedded grating in an elongated solid material optical waveguide includes a source that directs a coherent light beam of a frequency in the ultraviolet range in a primary path transversely toward the waveguide. A section of a diffraction grating extends through the primary path at a spacing from the waveguide, and the diffraction grating has a dimension normal to the primary path that exceeds the corresponding dimension of the primary path. Relative movement is effectuated between the waveguide and diffraction grating in unison, and the primary path, so that the light beam is diffracted at the diffraction grating into two mutually frequency shifted partial light beams propagating in diverging secondary paths.

Abstract: An optical waveguide light redirecting arrangement includes an optical waveguide having a solid portion that guides light in a first path along a longitudinal axis, with at least one grating region being embedded in the solid portion at a location remote from its end portions. The grating region includes a multitude of grating elements extending at such longitudinal spacings and at such oblique angles relative to the longitudinal axis to redirect light reaching the grating elements between the first path and at least one second path extending externally of the waveguide and diverging between a focus situated at a predetermined distance from the waveguide and the grating region. When light is directed in one of the first and second paths toward the grating region, it is redirected by the grating elements into the respectively other of the second and first paths with attendant in-phase combination in the other path of light having a wavelength within a range around a central wavelength.

Abstract: A bearing arrangement for rotatably supporting a generally cylindrical journal having an outer circumferential surface exhibiting out-of-round deviations superimposed on a perfect cylinder that is centered on a longitudinal axis, with the journal acting on the bearing arrangement with a basic radial action force aimed along a reference half-plane extending in a predetermined radial direction from the longitudinal axis, includes a pair of bearing pads situated at respective contact locations that are spaced in opposite circumferential directions from the reference half-plane. Each of the bearing pads extends substantially over the entire length, but at most only over a small fraction of the circumference, of the outer circumferential surface, such that the bearing pads are at most in a very limited area contact with the outer circumferential surface when the journal is supported thereon.

Abstract: A commutator arrangement includes a commutator member rotatably mounted on a support and including a plurality of circumferentially adjacent contact pads that are mechanically connected with one another and electrically separated from each other by respective intervening gaps, and a number of commutator brushes that are mounted on the support for only substantially radial movements toward and away from the commutator member and are biased toward the latter to establish contact between their respective contact surfaces and those of the pads. The lateral edges bounding one kind of these contact surfaces circumferentially deviate from those delimiting the other contact surface kind over at least a part of their courses such that different portions of such lateral edges are juxtaposed with their counterparts at different times during the relative rotation of the commutator member.

Abstract: An optical waveguide mode discrimination light filtering arrangement inclues an optical waveguide having an elongated multimode core, and a cladding that guides at least two modes of light of a given frequency in an elongated path along a longitudinal axis of said core. At least one grating region is embedded in the core at a location remote from the end portions of the core and has a multitude of grating elements extending with a substantially equal longitudinal spacing substantially normal to the longitudinal axis to reflect light propagating in the path and reaching the grating elements back into the path for longitudinal propagation therein opposite to the original propagation direction. The spacing of the grating elements is so related to the axial wavelength of one of the modes that the reflected light of the one mode interferes constructively while the light of any other of the modes passes through the grating region in the original propagation direction substantially without attenuation.

Abstract: An optical waveguide light tapping arrangement includes an optical waveguide having solid portions that guide light in a first path along a longitudinal axis, with at least one grating region being embedded in the solid portion at a location remote from its end portions. The grating region includes a multitude of grating elements extending with a substantially equal longitudinal spacing at an oblique angle relative to the longitudinal axis to redirect light reaching the grating elements between the first path and at least one second path extending externally of the waveguide at an angle relative to the longitudinal axis that depends on the oblique angle.

Abstract: A temperature compensated embedded grating optical waveguide light filtering device includes an optical fiber having an elongated core in which light is guided toward a core portion of a predetermined limited length that has embedded therein a multitude of grating elements extending with a substantially equal longitudinal spacing substantially normal to the longitudinal axis and collectively constituting a grating that reflects, of the light propagating in the path toward and reaching the grating elements, that of a wavelength within a narrow range about a central wavelength determined by the spacing of the grating elements and by the index of refraction of the material of the core as influenced by the temperature of and longitudinal strains applied to the grating, back into the path for longitudinal propagation therein opposite to the original propagation direction.

Abstract: An arrangement for detecting metallic particles carried by a fluid includes a metallic probe member which surrounds an elongated passage through which the fluid flows and which is constituted by a split tube having two marginal portions delimiting a gap which extends along said passage and completely separates the marginal portions from one another. Capacitors are arranged at the gap and alternating electric current is caused to flow in the probe member around the passage so that the probe member and the capacitors form a tank circuit having resonance characteristics that are influenced by any inclusion then present in the passage in a manner dependent on the electromagnetic properties of the inclusion. The character of any metallic particle then present in the passage is determined from variations in the alternating electric current that reflect the influence of such metallic particle on the resonance characteristics.

Abstract: A composite yet monolithic, free abrasive grinding lap includes a sintered porous matrix of ceramic or metal material and a quantity of silicon, substantially completely filling the pores of the sintered porous matrix preform at least throughout an effective region of the lap that is to come in contact with a workpiece to be acted upon by the lap. The free abrasive grinding lap is made by first slip-casting a preform, then freezing and freeze-drying the same, followed by lightly sintering the dry preform into a porous matrix preform, bringing the temperature of the preform to above the melting point of silicon, and filling the pores with molten silicon.

Abstract: A phase change material cooled mirror arrangement includes a mirror substrate which has a reflective front major surface and a rear major surface. The mirror is cooled by advancing at least one rod of a solid phase change material toward the rear major surface of the mirror substrate for gradual melting of the material at the rear major surface by heat absorbed from the substrate with attendant cooling of the latter, at an advancement speed sufficient for the solid phase change material to make up for the amount of such material that has been transformed into liquid by the melting thereof. The liquid phase change material is then removed from the vicinity of the substrate and possibly resolidified and added to the trailing end of the rod in a recirculating system.

Abstract: An optical waveguide light redirecting arrangement includes an optical waveguide having at least two solid portions each of which guides light in a path along a longitudinal axis, with at least one grating region being embedded in each solid portion. Each grating region includes a multitude of grating elements extending at such identical longitudinal spacings and at such an identical angle relative to the longitudinal axis as to redirect light reaching the grating elements between the path of one and the path of the other of the waveguiding portions.

Abstract: A variable light filtering arrangement includes at least one optical fiber section including a waveguiding core, and at least one permanent Bragg grating region in the optical fiber section. The grating region includes a plurality of grating elements constituted by periodic refractive index variations of a predetermined initial periodicity and cumulatively redirecting, of the light launched into the core for guided propagation therein, that having an axial wavelength within a narrow band around a central wavelength that is determined by the periodicity and refractive index variations of the grating elements. At least one of the periodicity and refractive index variations of the grating region is controlledly modified in such a manner as to temporarily change the central wavelength within a predetermined wavelength range.

Abstract: An arrangement for determining the magnitudes of selected physical quantities at a multitude of spaced locations includes an elongated optical fiber having a multitude of separate longitudinally spaced Bragg sensing gratings of substantially identical initial periodicity situated at such locations. Light pulses are launched into the core for propagation longitudinally thereof and for return from any of the sensing gratings of a detectable light echo at a central wavelength determined by the instantaneous value of the periodicity of the respective sensing grating that depends on the longitudinal stress applied to such grating as a result of the action of the physical quantity being monitored at the location of such grating.

Abstract: A thermal distortion effect compensated mirror includes a mirror substrate having a reflective surface, and a compensating layer on the reflective surface. The compensating layer is of a material that is substantially transparent to a laser beam to be reflected by the mirror, and has such a thickness as to substantially compensate, during the passage of the laser beam therethrough, for the differences in the propagation path lengths of different laser beam regions impinging on and reflected from different portions of the reflective surface that have been displaced to different extents from their original positions by different thermal growths of the respective underlying zones of the substrate owing to different heating of such substrate zones by different energy levels of the associated laser beam regions.

Abstract: An accelerometer arrangement includes an acceleration sensor that includes two capacitor plates having respective parallel mutually facing major surfaces which bound a sensing gap therebetween. A plate-shaped electrically chargeable proof mass is resiliently mounted in the gap in parallelism with the major surfaces for displacement in response to the action of acceleration forces thereon out of a substantially central rest position toward one or the other of the major surfaces depending on the direction of the acceleration forces. An electrical potential difference is established between the capacitor plates to generate respective electrostatic fields between the capacitor plates and the proof mass which cause a proof mass electrical potential variation having a magnitude and sense depending on the extent and direction of the displacement of the proof mass out of its rest position.

Abstract: A light-weight yet sturdy ceramic article, is manufactured by initially forming at least one fugitive core including a main portion and at least one holding portion projecting from the main portion and then positioning the fugitive core in a mold cavity bounded by a multitude of bounding surfaces so that the holding portion holds the main portion at predetermined spacings from all of the bounding surfaces. This is followed by filling the mold cavity around the fugitive core with a dense slip constituted by ceramic or metal particles in mixture with a liquid medium to form a ceramic or metal preform embedding the fugitive core in its interior and freezing the ceramic or metal preform, then the fugitive core is dissolved and escapes from the interior of the frozen ceramic or metal preform and finally the ceramic preform is converted into the ceramic article.

Abstract: Disclosed is the manufacture of a stress-free composite including reinforcing fibers embedded in and bonded to a matrix material such that differential contraction takes place in the matrix material relative to the fibers in response to temperature decrease. It involves embedding the fibers in the matrix material at an embedding temperature to obtain a composite precursor preparatory to subsequent consolidation thereof into the composite material at a consolidation temperature, and longitudinally stretching the fibers to such an extent that the longitudinal dimension of any portion of each fiber is substantially the same as that of the contiguous portion of the matrix material both at the consolidation temperature with the fiber stretched and at a predetermined operating temperature of the composite material in the absence of such stretching.